Building coral reefs in ancient times

540 million years ago, in the dawn before the Cambrian explosion, evolution was setting the stage for the global rise of animals. Before they took over the seas, the earliest animals developed strategies to defend themselves against predators. These strategies, which remain common today, include forming skeletons and building reefs. Penny et al. discovered a massive fossil reef deposit in Namibia made up of tiny coneshaped early animals known as Cloudina. The reef, which is 20 million years older than other ancient reefs, was probably formed as the Cloudina adapted to benefit from reefs, which protect the animals and allow them to feed more efficiently.

Abstract

Reef-building in metazoans represents an important ecological innovation whereby individuals collectively enhance feeding efficiency and gain protection from competitors and predation. The appearance of metazoan reefs in the fossil record therefore indicates an adaptive response to complex ecological pressures. In the Nama Group, Namibia, we found evidence of reef-building by the earliest known skeletal metazoan, the globally distributed Cloudina, ~548 million years ago. These Cloudina reefs formed open frameworks without a microbial component but with mutual attachment and cementation between individuals. Orientated growth implies a passive suspension-feeding habit into nutrient-rich currents. The characteristics of Cloudina support the view that metazoan reef-building was promoted by the rise of substrate competitors and predators.